Telephone-exchange system



Filed Sept. v422; 11 Sheets-Sheet 1 Oct. 28. l924. l,53,362

. L.. M. ALLEN TELEPHONE EXCHANGE SYSTEM I l med sept, 22. 1921 11 Sheets-sheep, 2

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l.. v M.. ALLEN TELEPHONE EXCHANG SYSTEM" I Fil'ed sept. 22 1921 11 shea 11 Patented @et 28,

LOUIS M. ALLEN, OF NEW YORK, N. Y., ASSIGNOR- TO "WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION OF .NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed. September 22, 1921. -Seral No. 562,471.

To all whom t may concern.'

Be it known that I, Louis M. ALLEN, a citizen of the United States, residing at New York, in the countyv of N ew York, State of New York, have invented certain new and useful Improvements in Telephone-EX- change Systems, of which thefollowing is a full, clear, concise, and exact description.

' This invention relates to telephone exchange systems and particularly to those systems wherein mechanical switching ap-` paratus is employed in the establishment of talking connections.

In exchange areas including both manual otlices and automatic oflices, where provision is made for the extension of calls made in a manual oflice to any of the outlying automatic offices, it is found desirable in some cases to have the selective switches in the called automatic office controlled from mechanism located at the calling manual office. By this plan the operator who first. answers the call is enabled to establish the interofice connection which leads to a distant mechani- 'cal oflice without assistance, the entire operation of the switches at the distant oflice being governed by mechanism at the originating oii'ice controlled by the answering operator therein.

At the manual office there are provided, a plurality of operators positions each of which has access to a plurality of groups of outgoing trunks, one group leading to each of the distant mechanical oiices served. lach position is further equipped with a sender controlling keyboard, a set of office keys and a set of indicating lamps for trunk identification. There is also located at the manual o'tllce a group of register senders, common to the use of all operators, and serving to control the movement of the switches inthe distant offices. ln order that an idle sender may be taken for use to extend a call,

and to associate such sender with the key-l board at the operators position concerned, and also with an idle trunk in the particular group leading to the called automatic oiiice, a plurality of switching units is employed. lhese units comprise three distinct parts: a sender selector for selecting an idle sender, trunk selectors for choosing an idle outgoing trunk and a plurality of operators position selectors. When one ofv the operators wishes -to extend a call an allotted one of these switching units is set in motion, the three different types of switches comprising the unit all acting simultaneously. v

Since the total number *of operators in the manual oliice greatly exceeds the capacity of a switch of the-kind desirable for use as a position selector the operators positions are divided into a plurality of small groups. Accordingly, the position selecting mechanism of each switching unit consists of a corresponding number of vseparate position selector switches. Each of the position selectors serves its own separate group of positions, whereby any unit has access to any position in the oiiice.

rIhe object of the invention is, therefore, the provision, in a system of the character above outlined, of a switching mechanism including a plurality of position selectors with means for selectively loperating said position selectors when the mechanism is taken for use. Y

A feature of the invention is the provision of means whereby, when a switching mechanism' is taken for use by an operator inany of the several groups, only that particular one of the position selectors having access to the operators position-.involved is set in operationA to select such position.

Other and further features contemplated in the present invention will be made obvious from a consideration of the descripf tion given hereinafter andalso from' the appended claims.

Referring to the drawing, Figs. l to 11, whentaken in the order shown in Fig. l2, disclose so much of a telephone system embodying the principles of Vthis invention as is necessary to a comprehensive understanding thereof. F i0. l shows one of a plurality of answering operators` positions in Y a manual oflice provided with cord circuits for extending subscribers lines over interoliice trunks outgoing tothe distant mechanical offices. One of these outgoing trunks terminating'in a distant mechanical office is also illustrated -in this figure.

Figs. 2, 3, 4 and 5 show the switches which constitute one of a plurality of Switching units. Figs. 2 and 3 illustrate two of'a series of trunk selectorswitches for selecting idle trunks outgoing to'a particular mechanical office. Fig. 4. shows a sender selector switch having access to a groupV of common register senders. Fig. 5 shows an operators position selecting mechanism which consists of a plurality of sepa-rate position selector switches, two of these switches being shown in detail in the drawing.

To the right of the right-hand broken line in Fig. 6 there is shown an operators position provided with oilice keys and a series oi sender control keys. Between the two vertical broken lines another operators position belonging to the same group of positions as the one shown at the right oi the ligure is also schematically illustrated. To the extreme leiit of this Vtigure there is shown a third operator-s position which is position No. 1 ot the lilith group. Fig. Y shows a set of indicating lamps located at the operators position illustrated at the right in Fig. 6, the function ot which is to give the operator a visual identification of the selected trunks at her position. Fig. 8 shows a starting and an allotting mechanism common to the entire Agroup oit switching units individual to the outgoing group ot trunks to the mechanical ohce illustrated.

Figs. 9, 10 and l1 show one oit a plurality ot register senders located in the manual oflice and common to all operators positions Yfor controlling the selective movements ot the switches in the distant mechanical oliices. Fig. 9 shows a register control switch and its associated circuits. Fig. 10 shows a set ot relay registers upon which the designations ot' called lines are recorded from the operators position. Fig. 11 shows the sender consisting of a series of counting relays and a circuit changing switch.

lilhile the invention has heen disclosed herein in combination with an indicating device tor indicating to the operator the numlier ot the trunk selected and with specific mechanism comprising a plurality ot trunh selector switches 200, BOO, etc., and a steering switch tor enabling the selection of an idle trunk in a large group oit trunks, it is to he understood that applicant does not claim these features as a part of his invention but has disclosed them herein only for the purpose of more clearly illustrating the manner in which his invention is to he practiced. rlhc trunk indicating dev-ice has been made the subject of a separate application, Serial No. 715,511, liled May 24,19% in the naine of H. lV. lsacDougall andthe trunlt selecting mechanism has-.heen made the suhject of application, Serial No. Z1/1,999 tiled May 22, 1924 in the naine oit lV. C. Weai'eix General description of appt/rotas Cmd operati/0a..

The selective switches 123 and 12st, located in the distant mechanical oiiice 122, are ot the well-known power drive type such as that shown in the patent to Craft and Reynolds, No. 1,123,696, issued January 5, 1915.

The trunk selector switches 200 and 300, the sender selector 4:00, the position selectors 500 and 510, the allotter switch 800, the register control switch shown in Fig. 9, and the sender control switch shown in Fig. ll are all of the rotary single motion step-bystep type driven by stepping magnets 'trom terminal to terminal and so arranged that the brushes are moved forward to the next terminal upon deenergization of the stepping magnet.

in 'the system disclosed connections are established hg.' the operators in the manual origina oiliceto any of aplurality oi distant inechacal otlices. For each mechanical oice to which the operators in the iuanual utilice have access there is provided a group ot intcrconecting trunk lines terminating at the mechanical otlice in machine switches. .fit the n'ianual oiiice these trunks are mutipled so as to appear in lachs 'oe-- iorc cach oft 'the openr ors positions. The ope tor responds to an incoming call in the usua. manner and upon ascertaining the name oft the called office and the number ot the war-.ted line therein, she manipulates the necessary apparatus at her position which causes the automatic selection oi an idle trunk outgoing to trie called o'tlice, the association ci idle register sender with her voelt-ion and with the selected trun r and the isual indi ion on indicator lamps ot the dentity oi the selected trunk. She 'then iets up the number of the called line on a reyhoard at her position and completes the coinicctiini hy inserting the calling plug ot her cord circuit into the jack oi the indicar-cd outgoing trunk. The manipulation ot the opera nfs keyboard causes the desired des' jnation to he registered upon the registers oli the associated sender which thereafter serre to control the automatic switches in the distant `iimechanical ottico to further extend the outgoing selected trunk to the called subscriber@ line.

.is ahovc noted, there is a group oi outgoing trunks Vfrom the manual ohce to cach oil" thc distant mechanical ollices served. Only one of these distant mechanical oilices. the one illustrated at 122 in the drawing and one ot the trunks 1525, 12T leading therehave heen shown herein. For the Orc-ui) ,z trunks leading to the oilice 122 there il: n orided in the man otlice plufalitgT ot vhing units, only e of which shown js. t and t. Yrllhile these swx :china are indiridual to a single group oil" Herent inecha' ual fons in the manual oiice. iiachioltB g units comprises series ott-rui... selector swi'ches, two ot which are shown at 300 and 200 respectively.

.ming that tue outgoing group ot switchino' lll) trunks lo the oliice 122 is niade up ot 160 trunks, there will be provided in that casey eight trunk selecting switches each having a capacity for twenty trunks. The switch 300 serres the liisttwenty trunks in the groiil'), the switch 200 serves the-second twenty trunks, and so on tor the remaining si); selector switches. The switch 300 coinprises a stepping' magnet 301 anda plurality of brushes 302, 303, 304, S05, 306, and 307 and their cooperating terminal banks. Similarly, the switch 200 consists of a stepping magnet 201 and brushes 202, 203, 204, 205, 206 and 207 and the corresponding terminal banks. rThe saine is true oi' the si-icceeding selector switches not shown.

ot the selector switch 300 cooperate, and the banks with which brushes 206 and 207 of switch 200 cooperate, and the corresponding banks ot all succeeding switches in the series have their terminals miiiltipled, as `illustrated, For a purpose which will become obvious l from the following` description` tfoniiiion to the entire series of trunk selector switches Athere is provided a steering or side switch 210 consisting of stepping n t net 221, brushes 222, 223, 224, 225, 226 and 227 and their cooperating terminal banks. The purpose or" the side switch 210 is to determine the first. one of ther series of trunk selectors to betaken tor use and to govern the circuit` changes during the transition troni one vselecto-r switch to thel next. Provided all trunk selectors are in their iioinial positions when a switching ii'iit is taken ii'oi use, the first one ot thesi itches in the series, namely the switch 300 r.' il bc set in motion to hunt or an idle trunk in the first group of twenty. It all these trunks ai'el'iusy the switch B00, having inoi'ed its hrushes completely over their hank termina ls, Causes the advance oi' the side switch 210 to its next position where the second trunk selector in the series is then sltectlrcand operates to search for an idle trunk in the. second group oit' twenty. This =i"ei'liiie continues until an idle trunk is d. The side switch 2.10 has no i" ny hut re ns in the position to the k selector switch Le series i idle trunk instead oitccininenciiig again at the beginning ot the series.

lii addition to the trunk selector switches, the switching unit also consists of a sender selector switch 400 comprising `a stepping magnet 401, brushes 402, 403, 404,v 405, 406 and 407 and their corresponding terminal banks.

Lastly, the switching unit includes, together with the trunk selectors and lthe ser der selectors,a plurality of operators rlf'he tern'iinalA banks with which the brushes 306 and 507` Aunit shownis to associate any I :tour

f tions., Since there are a plurality oi switching et in motion to search for an position selector switches, -two of which are shown at 500 and 510. The switch 500 coinyprises a stepping magnet `507, brushes 501, 502, 503, 504, 505 and l506 and their corresponding terminalbanks, while rthe switch 510 similarly consists oit a stepping magnet 517 together with brushes 511, 512, 513, 514, 515 and 516. In order to secure a better understanding of the purpose for dividing the position selectin@ mechanism up into a plurality of selector switches each separate and distinct from the other, an explanation will lirst be given of the plan on which the operators vided. Y Y

Assume that the manualoliice has 100 operators positions, which is a greater number than a single position selectorswitch of the usual type can serve with the requisite speed and efficiency. Accordingly, the total number of 100 operators positions is 4divided into live different groupsot twenty positions each, and each ot theswitch ing 'units is provided with live position selector switches each having a capacity for twenty operators` positions. The position selector 500, for ex ample, serves the rst group of twenty operators ypositions in the oce. The first and second of these positions in the first group of twentyare illustrated at 600 and-.610. The next three succeeding position selector switches, which are not shown in the drawing, serve thel next three groups of twenty operators` positions. Finally, the last or fifth position selector switch 510serves the lifthj group of twenty operators positions, the first position of which is schematically shownjat 620 of Fig. 6. The function ol: the position selector switch 500 of the switching one oi the twenty positions with the ri-gister sender selected by the switch 400ml' the 'ne unit vand to associate the trunk indicating incclianisni'iii Fig. '7 at the operators position with the controlling devices pertainingto the trunk selecting siif'itchos ot the saine unit, and which are shown .in 3. lukewise, this is the-function ot the remaining position selector switches oi? this switching unit with respect to the .succeeding four groups of twenty operators7 posim ot' operators positions. Where these switching units are all equivalent to one another and may be taken for use by any one of the operators in the exchange, an allotting device is employed for allotting an idle switching unit for the use of any operator and for preif'enting more than one switching unit being taken for use at the same time.y rThe allotter tor this purpose is shown in the :torni of the switch 800 in Fig. 8. Switch 800 consists ot a stepping magnet 801, brushes 802, 803, 804i-, 805` F306 and 807 and their corresponding terminal banks. The brush 807 and its terminal. bank pertain to the iirst position selector switch 500 of each of the several equivalent switching units. The brush 808 and its terminal bank pertain to the litth or last position selector switch 510 ot each ot the switching units. Similarl the intermediate brushes 806, 805 and 801i pertain, respectively, to Athe three intermediate position selectors ot each switching unit belonging to the outgoing group Vot trunks leading to the mechanical oflice 122.

The balancing coil 812, together with the polarized relay 8111, acts to initiate the operation oi' the allotted switching unit under the control of any operator in the irst group of operators. The balancing coil 813 and polarized relay 815 act to initiate the move- O ment ot the allotted switching unit under the control of any operator in the last or tth group ot operators. Likewise, three intermediate balancing coils are provided, not shown, and serve, respectively, to start the allotted switching units under the control 01"' operators in the three respective intermediate groups. rllhe tive balancing coils are individual, respectively, to the tive position selector switches ot each switching unit. For example, the coil 812 is individual to the position selector 500 having` access to the {irst group ot twenty operators positions. rlhe coil 813 is individual to the :fifth position selector switch 510 having access to the iiitth group ot twenty operators positions. The saine is true ot the remaining balancing coils and position selector switches.

The register sender, shown in Figs. 9, 10 and 11, is the usual type used in central x,s tor governing the selective movement rcvertive control power driven switches, such as those illustrated at 123 and 124. l e basic principle ot a set ot counting reis, which. are successively energized under control ot impulses reifer-ted from the switch over the tundament-al circuit, the number of counting relays operated being dependent upon the designation recorded on the registers to determine the extent ot motion of the switch, is employed in the sender shown in this system and the description to be given in connection with the operation hereinatter is thought to be sufficient.

Each ot the several operators positions is equipped with a plurality ot keys individual to the different outlying mechanical otlices tol which connections may be extended Jtroni the manual ofiice. The keys 601, 621 and 627 at each of the three positions shown in the drawing are individual to the mechanical oiiice 122.` The manipulation oi one ot these keys by the operator at the corresponding position initiates the movement of the allotted switching unit individual to the group of trunks outgoing to the office 122. For every other mechanical oiiice, similar to the ottico 122, served through the manual otice illustrated in this disclosure, there will be at each operators position an oiiice key similar to those shown. The actuation of these keys will, in a similar manner, cause the movement of an allotted switching unit, similar too the one shown in Figs. 2, 3, 4 and 5, but individual to the particular distant mechanical office represented by the key depressed.

Dem'lcd descrprz'on 0] ope/ration.

A. general description having thus been given of the system and its purposes, a detailed explanation will now be made with respect to the establishment of a telephone connection. To this end it may be assumed that the subscriber of line 100 in the manual otce wishes to converse with the subscriber of line 125 in the distant mechanical ofiice 122. Upon removing his receiver from the switch hook the calling subscriber completes a circuit for the energization of line relay 104, which, in turn, causes the illumination ot lamp 105. It will be considered that the line 100 terminates in jack 101 before the second operator in the iirst group of twenty operators. rilhis operator, on observing the illumination of lamp 105, answers by inserting the plug 102 oi her cord circuit in the jack 101. The insertion of the plug in the jack completes a circuit from battery through the lamp 10'?, resistance 106, sleeve ot plug 102, sleeve of jack 101, winding oi relay 103 to ground. Relay 103 operates and severs the circuit of relay 104 which causes the deenergization ot the line lamp 105. The receiver being oii the switch hook, the insertion of the plug in the jack also conipletes a circuit 'from battery through the lower lett-hand winding ot repeating coil 109. winding oi relay 110, ring of plug 102.y ri', ot jack 101. over the loop ot the line, returning through the tip ot jack 101, tip ot plug 102. upper left-hand winding ot repeating coil 109 to ground. Relay 110 opcrates in this circuit and closes a circuit troni battery through its Contact and armature. resistance 108, resistance 106, thence over the path previously traced through the winding of relay 103 to ground. This latter circuit shunts the supervisory lamp 107 causing the same to remain extinguished.

The operator next depresses the listening Versational relation with the calling line and ascertains the desires ot the calling' subscriber. llpon learning that he'wishes to tall; with a subscriber in a distant mechanical office 122, the operator, whose position is shown at 610 in Fig. 6 of the drawing, actuates the otlice key 601 which bears the name of the othce 122. The depression of key 601 completes a circuit from ground through the outer back contact of relay. 611, left-hand contact ot key 601, right-hand winding of relay 602, right-hand winding of relay 603, Contact of relay 613 to battery. Relays 602 and 603 operate in this circuit and close a holding circuit for themselves as follows: battery, through the contact oit relay 613, right-hand windings of relays 603 and 602, inner lett contact of relay 602, inner back contact or" relay 612, inner front contact of relay 603 to ground. The de- Y pression of key 601 also closes a circuit from battery through the winding of relay 609, inner back contact of relay 611, right-hand r contact of key 601 to ground. Relay 609 operates and closes a circuit from battery through its' winding and the winding of relay 611 in series, front contact of relay 609, outer left contact of relay 603 to ground. Relay 611, which is shunted as long as key 601 is held actuated, operates in series Vwith relay 609 over the circuit just traced at the instant the operator releases the key 601. The operation of relay 603 closes a circuit from battery through the' right Contact of said relay, resistance 608, lamp 607, outerA lett back contact ot relay 606 to ground.-

rllhe lamp 607 illuminates and remains lighted under the observance of the operator until an idle register sender has become associated with her position. y

Immediately that relay 602 is energized a circuit is closed from battery through resistance 614, outer contact ot'relay 612,'outer lett Contact of relay 602, conductor 821., thence to a point between the lower winding of the balancing coil 812 and the polarized relay 814. The iow ot currentto ground through the coil 812 and through the winding o the polarized relay 8111 is in such a direction as to cause said relay to attract its armature. Relay 814 closes a circuit from battery through its Contact, winding ot relay 809, normal contacts of said relay, contact of relay 811 to ground. Relay 809 operates and closes a lockingl circuit for itselt through its inner lett contact to ground. Relay 809, at its outer left contact, closes an energizing circuit for relay 811.. Relay 811 attracts its armature and removes ground from conductor 823 thereby preventing the operation of another relay similar to relays 809 and 810 until the allotted switching unit has been started and another one allotted in its stead. Relay 809, on operating, closes a circuit troni ground through the contact of relay 808, right front Contact of relay 809, brush 807, conductor 820, leading to the switching unit which'is allotted by the allotterswitch 800 when standing in the position shown, winding of relay 508 to battery. Relay 508 operates and closes a locking circuit for itself from batter f hrough its winding and inner left contactto ground at the contact of relay 521. ground through` its outer'right front contacts, conductor 535, lett back Contact ot relay 520, and thence in parallel through the winding of relay 519 to battery and over conductor 536 through` the left-hand winding ot relay 108 to battery'. Relay 519 operetes and locksV in a circuit from battery through its windingk and inner left contact, conductor 530, lett contact'of relay 409, outer lett contactl of relay 410,1conductor 4123, outer left back contact of vrelay 525 to ground. Relay 408 also energizes and locks battery through its winding and inner left contact, conductor 535-to, ground at the outer right contact Y of relay 508. rRelay520 at this time applies a ground potential to the conductor 8l6rwhich serves to render the switching unit busy to the allotter switch 800 and also initiates the movement of the allotter to se- Vlect and allot the lnext idle switching unit for use. be considered at a later point in the description. Relay 520 also closes a circuit from battery through Contact of relay 520 to ground. Relay 522 becomes energized and loclrsin a circuit from battery through its right-hand winding andl right-hand front contact, front contacts lof the inner right-hand armature of relay 508, l

brush 501and its normal, position terminal,

rlhe oper-ation of the allott'er will the left-hand windino of relay 522, normal contacts at the inner efthand armature of relay 523, outer right front 75 j Relay 508 completes a circuit troni outer rightfront contact of relay 508 to i ground. Relay 522 also closes a circuit from batterythrough the right-hand winding of relay 523, left-hand con-tact of relay 522, contact of relay 521 to ground. Relay 523 operates and locks ina circuit from battery through its left-hand winding and outer right rontcontact of relay 520 to ground. With relays 522 and 523 operated a circuit is closedfor the stepping magnet 507 of the position selecting switch 500, which has accesstothe first group of twenty operators positions containing position No. 2,.shown at 610, at which the depression ot key 601 rsu has initiated the movement of the switching unit. "llhe lcircuit .tor the magnet 507 may be -traced 'from battery through the Winding and contact of said magnet, inner right front contact of relay 508, right contact ot relay 523, Vlett 'front contacts of relay 522, contact ot relay 521 to ground. Magnet 507 interrupts its own circuit and advances the brushes 501, 502, 503, 504, 505 and 506 from position to position in the direction indicated by the arrows. The test brush 501 tests the condition ot the successive operatorsj positions. The terminals Witi Which brush 501 cooperates, representing non-calling positions, will present a ground potential to the brush 501. This ground potential serves to maintain the holding circuit ot ,relay 522, above traced, closed. lllhen, howeifer, the brush 501 reaches they second position terminal, representing the second operators position 510, no ground potential Will be found thereon cue to the energized condition ot relay 602. Hence, the circuit of relay 522 is opened and this relay becomes deenergized, opening, in turn, the operating circuit of the stepping magnet 507 whereby the switch 500 comes to rest. Immediately that relay 522 releases its armatures a circuit is closed from battery through the right-hand Winding ot relay 612, right front contact oi' relay 602, conductor 632, brush 501, front contacts of the inner right-hand armature ot relay 50S, right back contact of relay 522, Winding o1 relay 524, outer right contactlotfrelay 519, outer left contact of relay 528 to ground. Relays 512 and 524 become energized. Relay 612 closes a holding circuit for itself from battery through its left-hand Winding and inner left front contactto ground at the inner lett contact of relay 603. Tdelay-612 also opens the previously traced locking circuit ot relays 602 and 603 but these relays remain energized in a substitute locking circuit traceable from battery through the contact of relay 613, left-hand windings of relays 503 and 502 in series, Vfront contacts at the right-hand armature oit relay 602, conductor 632, and thence to ground through the Winding of relay 524, as above traced. Relay 612, at its outer lett contact, disconnects battery from the conductor 821 and the balancing coil 812.

Relay 524, Which energizes in series With relay 612, completes a circuit from battery through the Winding of relay 526, contact ot' relay 524,V outer left back contact of relay 525to ground Relay 525 operates and closes a circuit trom battery through its Winding and the Winding of relay 525, right contact of relay 525, conductor 537-, innen contact. of relay 410, innerl lernt. contactot relay 40S to ground. Relay 525, however, cannot operate in this circuit since it is shunted by lthe direct circuit traced Jfrom battery through the Winding of relay 525 and the contact ot relay 524 to ground. lWith relay 526 operated a circuit is established troni battery through the right back contact ot relay 525, lett contact of relay 526, Winding of relay 527 to ground. The operation ot relay 527 serves as an indication that the operators position has been Jround.

The selected operators positionis maiutained non-selectable to other position switches by the application of ground potential to the test terminals of all .sv-.'itches` similar to 500, with which the brushes i cooperate. lt will. be iuiderstood, ot course, that the terminals ol? the position selector switches are inultiplcd to the terminals in corresponding switches oi other units. The circuit tor the application ot' this ground potential to the mutiple test terminals olt selector 500 and its corresponding selectorsl in other switching units may be traced troni ground through the outer lett Contact oi" rclay 523, outer right contact relay 510, Winding ot relay 524, right bach contact oi relay 522, front contacts at the inner right armature of relay 508, brush 501, and thence to the multiplel terminals representing the operatorls position selected. rllhe resistance or.' relay 524 is comparatively low so that the potential on the test terminals acts to render the position non-selectable to othcil switches.

T he relay 408, Wnich energizes at the time the oiiice key 601 is depresset, serves to initiate the movement ot the sender selector switch 400 to select an idle register sender. Upon the operation ot relay 408 a circuit closed from battery through the right-hand wnding of relay 412, normal contacts at the inner right ari'nature ot relay 413, inner right front contact of relay 408, right contact or relay 409 to ground. Relay 412 energizes and closes a loclring circ-uit for itselit as follows provided the register' sender, upon the terminals oli which the brushes ot the selector 400 are noiv standing, is busy: battery, through the lett-hand Windin and lei't front contact oit relay outer left contact oit relay 408, contr r 119, test l sh 407, test terminal oi the busy sender, and thence to ground. llelay 412, on remaining energized, closes a circuit from battery through the Winding ot relay 413, right contact oi' relay 412 to ground. llelajf 413 operates and closes a circuit for itseliIIV trom battery through its Winding and inner right Contact, inner right Contact of 408 to ground at the right Contact ci r' y 409. lelay 413 opens the energizing circuit through the right-hand Winding ot relay 412 whereby this latter relay is nov7 dependent Vlor its continued energizat-ion upon the test circuit through its left-hand Winding and the test brush 407. llllith relays 412 and 413 both energized a circuit is established Afrom battery tl'irough the winding and contact ot the stepping magnet 401, outer right contact of relay 413, right front contact ot relay 412 to ground. Magnet 401 opera-tes to advance the brushes ot the switch 400 -ifo-rward to their next position terminals. The magnet 401 interrupts its own circuit and continues to advance the brushes of the .sender selector switch until the test brush 407 encounters a non-grounded terminal identifying an idle register sender.

et the instant an idle sender is reached the holding circuit of relay 412 is opened and this relay becomes deenergized to open the stepping circuit ot magnet 401. Relay 413, however, remains energized. 1When relay 412 becomes deenergized a circuit is closed from ground through the lett contact or" relay 41B,y winding ot relay 414, lett back Contact oit relay 412, outer lett Contact of relay 408, conductor 419, test brush 407, conductor 424, outer left bach contact of relay 900, thence in parallel through the resistance 902 and the winding/of `relay 901 to battery. Relay 414 operates in this circuit and establishes a circuit 'from battery through the winding of relay 415, outer riglit bach contact of relay 416, contact of relay 414 to ground. Trelay 415 operates and closes a circuit from battery through its winding and the winding ot' relay 416 in series, inner left contact of relay 415, conducto-r 538, inner left contact of relay 408 to ground. i Relay 416, however, cannot operate at this time since its winding is sliuiited out by the direct path to groun'l at the contact of relay 414. Relay 901, which also operates in series with relay 414, closes an obvious circuit for relay 903.

The relay 415, which operates at the tim theV switch 400 selects an idle sender, serves in conjunction with the relay 527, which is operated at this time provided the operators position has been selected, to complete a circuit for the connecting relay 529.

This circuit may be traced :trom battery through the winding of relay 529, outer right contact oit relay 527, conductor 539, outer right back Contact of relay 418,'outer lett contact of relay 41,5, conductor 588, inner left contact of relay 408 to ground. Relay 529, at its armatures and contacts, extends the three conductors 420, 421 and 422 from the selected register sender through the brushes 504, 505 and V506 to the operators keyboard whereby the manipulation of these keys will serve to record the designation oi" the called line on the registers of the sender. c

At the time the sender is selected a circuit is closed from ground through the outer lett contact of relay 608, inner lett back Contact of relay 606, winding of relay 605, inner left back contact or" relay 604, brush 505,middle Contact ot relay 529, conductor 421, brush 405, conductor 915, brush 912 of the control 'Relay 604 connects the operators keyboard,

shown at the right of Fig. 6, to thethrce control conductors 420, 421 and Relay 604 also establishes a circuit from battery through theright contact of relay 608, rcsistance 608, outer left front contact oi relay 604 to gr-ound. This circuit shunts the current away from lamp 607 and causes the same to become extinguished which serves as an indication to the operator that a sender has been selected and is now in condition to receive the'record of the called subscribcrf-i line.

The operation of relay 408, which causes the movement of the sender selector switch 400, also serves to initiate themovement or a trunk selector switch for the purpose ot Vselecting an idle trunk leading to the me chanical oiieice 122. It will be observed that ll three switches, namely theoperators position selector, the sender selector, and the trunk selector are operated simultaneously.

Assume that all trunk selector switches 300, 200, etc. are intheir normal positions at the time the switching unit is ,taken torv use. Accordingly, the side switch 210 will be standing with its brushes 222, 223, 224, 226 and 227 upon the No. 3 terminals ot' the corresponding banks.` Positions 8 to 10, inclusiye, ot the side switch represent, respe tively, the reight trunk selector switches in order. Terminals 11 to v18 also represent,

respectively, the yseries of eight trunk sev lector switches and laccordingly these tsrN niinals are multipled to terminals 8 to .10, as shown in the drawing. in this manner the side switch controls in a single revolution two successive V'operations of the entire series of eight trunk selector switches. l/Vith the iirst trunk selector 300 in its nor-r mal position andwith the side switch 210 in position 3, theV operation of relay 408 causes the closure of a circuit from battery through the winding of stepping magnetv 301, inner contact of said-magneu conductor 216, No. Sterminal 228, brush 223 ot the side switch, conductor 820 outer right contact ot relay 408, yright bach contact-of relay 311,'

conductor 321, brush 224 and its ilo. 8 terminal, conductor 2.18,V test brush 303 and its No. 21 terminalv ,to ground. A parallel branch of this '-i'rcuit leads through the winding of relay 311, conductor 25, to ground at the inner left contact of relay 108. Relay 311, however, does not operate so long as its vinding is shunted by the direct path to groimd Vat the test brush 303. The stepping magnet 301 interrupts its own circuit and advances the brushes of the switch 300 to their No. 0 position terminals, which rep.- resent the irst trunk in the lirst group ot twenty. lf the lirst trunk is busy a ground potential will exist upon the No. 0 test terminal and the stepping magnet 301 is again energized. Assume that all trunks of the lirst group of twenty are busy. This being the case the brushes or" the selector switch 300 are stepped arouinl until they reach their No. terminals. lflhen these tcrminals are reached a circuit is closed 'from battery through the winding ot stepping magnet 301, conductor 21e, brush 222, conductor 319, the No. 20 terminal 323, brush 300, conduct-or 327, neXt to the inne-r Contact of relay 528 to ground. Magnet 301 becomes energized and remains energized in this closed circuit. @n attracting its outer armature the magnet 301 establishes a circuit from batteryy through the winding and contact of magnet 221, brush H25 and its No. 3 terminal, conductor 220, outer Contact ot magnet 301, conductor 212, brush 307, conductor 326, innermost back contact or relay 528 to ground. Magnet 221 becomes energized and interrupts its own circuit and advances the brushes 222, 223,224, 225, etc. ot the side switch 210 from their No. 3 to their No. e terminals, in which position they are shown in the drawing. is brush 222 disengages its No. 3 terminal the above traced circuit ot magnet 301 is opened and this net becomes deenergized to advance the brushes of the first selector switch 300 to their No. 21 terminals, or to their normal position.

immediately that brush 22a` encounters its No. 1- terminal a circuit is completed from battery through the winding and inner contact oit stepping magnet 201, conductor 215, brush 223, and thence, as previously traced, through the right back contact of relay 311, conductor 321, brush 224-, conductor 217, brush 203 and its No. 21 terminal 229, to ground. Magnet 201 interrupts its own circuit and advances thebrushes of the selector switch 200 on to their No. 0 terminals, testing the condition of the iirst ot the second group of twenty trunks. iissumingthat allV trunks preceding the trunk No. 31 are busy therefore, the magnet 201 continues to advance the brushes until they reach the terminals of this idle trunk at which time no ground 'potential is found on the terminal engaged by test brush 203. Due to the absenceo ground potential on the test terminal, the stepping circuit for the magnet 201 is opened and the switch comes to rest.

Laissez the selected trunk in all other trunk selectory switches. ln this manner the outgoing trui 120, 127, which has just been selected by the selector switch 2,00, is rendered non-available to any other switch. Relay 311, furthermore, completes a circuit from ground through its outer lett contact, conductor 329, inner right contact oit relay 527, winding oit relayY 52H to battery. Relay 523, the circuit ot which it is to be noted depends upon the tact that the operators position selector has found the position and the trunk selector has found an idle trunk, serves to extend certain control conductors through from the trunk selector switches to the indicating equipment at the operators position. Relay 523 completes a circuit from ground through its innermost front contact, conductor 426, right contact of relay Z115, normal contacts at the inner left armature of relay 310, and winding ot said relay to battery. Relay 310 operates and locks in a circuit trom `battery through its inner left front contact, conductor 534-, inner left contact of relay 403 to ground.

Operation of tru/nk indicating mecha/imm.

The complete switching unit has thus been operated and an idle trunk is selected, an idle register has been chosen and associated with such trunk and also associated with the particular operators position on which the movement ot' the switching unit was initiated. The next operation to be le scribed is the indication on the lamps at thc operators position of the identity of the trunk that has been chosen in order that thc operator may complete thc connection o.' the called. line over this trunlr. lfipontheopn eration et relay 528 a circuit was closed lrom ground through the right-hand high resist ance winding of relay 312, brush 227 and ils No. 4- terminal, conductor 323, inner left baci; Contact of relay 3141, conductor 325, nent to the outermost contact ot relay 523, brush 503, conductor 701, right back contact o1" relay 702, left-hand winding of sensitive relay 704-, left-hand winding ot marginal relay 706 to battery. .lelay T0- operates but due to the high resistance of the right hand winding of relay 312 the marginal relay 706 remains inert. Relay i" 041: loclrs in a circuit from battery through its righthand winding and right contact, conductor 720, inner left front contact of relay 603 to grrnmd. itt the same time a circuit is closed lill 705 are energized.

from ground through the left-hand low resistance winding of relay 312, brush 226 and its No. 4 terminal, conductor 322, outer lett back contact ct relay 314, conductor 324, outermost contact or' relay 528, brush 502, conductor 700, inner' lett bach contact of relay 7 02, left-hand winding of sensitive relay 703, left-hand winding of marginal relay 705, conductor 722, right contact of relay 603 to battery. Due to the low resistance of the lett-hand winding of relay 312 both the sensitive relay 703 and the marginal relay Relay 703 locks in a circuit from battery through its right-hand winding and inner right contact to the grounded conductor 720, while relay 705 locks in a circuit from battery through its right-hand winding and inner right contact, conductor 723 to ground at the outer left Contact of relay 603. rIhe relay 312 becomes energized in the circuit traced and completes an obvious circuit for the relay 313. Relay 313, on operating, closes a holding circuit from battery through its winding and right contact, conductor 330, conductor 426 to ground at the innermost front contact of relay 528. Upon the energization oi"- either of the relays 703 and 704 a circuit is closed over the inner lett Contact of one of the other of these relays through the winding of relay 703 to battery. It may be observed that either relay 703 or relay 704, or both, will he operated 'for every position that the side switch 210 may take. ln other words, regardless of the group of twenty trunks in which the idle trunk is selected, the combination of the marginal and sensitive relays operated due to the position of the side switch will always include one or the other orboth of the relays 7 03 and 704. Consequently, relay 702 is always operated. rlhis relay is constructed so as to be slow in attracting its armatures and also slow-to-release. As soon as relay 702 becomes energized it opens the circuit of relay 312 and this latter relay releases and closes a circuit from ground through its bacl: contact, lett contact of rela 313, winding of relay 314 to battery. Relay 314 operates and disconnects the control conductors 324 and 325 from the conductors 322 and 323 leading to the side switch and connects them instead to the conductors 326 and 327, which extend in multiple to the corresponding brushes of the trunl; selector switches.

A. circuit is now established from ground through the left-hand winding of marginal relay 714, lett-hand winding ot sensitive relay 715, inner right baclr contact of relay 719, inner left front contact of relay 702, conductor 700, and thence, as traced, to conductor 324, outer left liront Contact of relay 314, conductor 327, conductor 317, brush 206, terminal 230, conductor 316, `conductors 331 and 332, right Contact of relay 314,

inner left contact of relay 311, conductor 531, outer left contact of relay 527 to bat'- te-ry. high resistance, both relay 715 and marginal relay 714 are energized. These relays lock in circuits through their right-hand windings to the conductors 720 and 723, respectively. y Furthermore, a .circuit is closedl from ground through the left-hand winding of sensitive relay 716, left back contact of Since the circuit traced includes no relay 719, right front contact of relay 7 02, v

conductor 7 01, thence through the conductor 325, inner left front contact of relay 314, conductor 326, conductor 318, brush 207, terminal 231, conductor 315, lefthand low resistance winding of relay 308,

normal left contact of relay 309, conductory 332, right contact of relay 314, inner lett contact of relay 311, thence over conductor 531 to battery. Relay 716 operates and locks through its right-hand winding tothe grounded conductor 720. Relay 308 also operates in this circuit and closes a circuit from battery through the outer lett contact of relay 527, conductor 531, inner left contact of relay 311, right contact of relay 314, conductor 332, normal left contacts of relay 309, lett contact of relay 308, winding of relay 309, conductor 330, conductor 426 tot ground. Relay 309 attracts its armatures and closes a. locking circuit for itselfv closes a` circuit for relay 718 and this lattery relay, in turn, closes a circuit from battery through the Winding of relay 719, contact of relay 718, and thence to ground at the inner left contact of either relays 715 or 716. Relay 719, upon operating, opens the circuit of relay 308 permitting the same to release its armatures. A circuit is then closed from ground through the right contact of relay 309, right contact ofv relay 308, conductor 326, inner le'lt front contact of relay 314, conductor 325, next to the outermost contact of relay 528, brush 503, conductor 701, right trent contact of relay 7 02, left front Contact of relay 719, through the windings of relays 708 and 709 in parallel, to battery. Relays 7 08 and 709 become energized in this circuit.

lifith the lamp controlling relays operated in the combination above described, 'the proper lamps are selected and illuminated 

